Electromagnetic radiation incident on reflective surfaces is reflected according to known and well understood principles. These principles are widely used in design of antennas and test bodies, as well as in receivers for radar systems.
One set of problems presented by these principles becomes important at the termination edge of a reflective surface. There, where it terminates abruptly, will be a very strong diffracted field. It is quite perceptible when the reflective body is illuminated by the radiation, and facilitates detection of the surface and its body. Also, where these edges occur in antenna, undesirable sidelobes and backlobes are created, which can seriously perturb the focused fields in the testing or quiet zone.
It is an object of this invention to provide a reflective surface which reduces the abruptness of the terminal edge, thereby substantially eliminating the diffractive field of a reflected wave at that edge. This renders the terminal edge less visible, and in some applications greatly reduces the formation of backlobes and sidelobes.
Another set of problems presented by these principles resides in the fact that the size of a continuous metal object is readily deducible from the properties of the reflected radiation. It can be useful to change the perceived size of a body, not only to confuse an observer, but to provide for versatility of design. It is therefore another object of this invention to provide a surface which behaves as a piece of metal that changes its perceived size and response as a function of the frequency of radiation incident on it.
This invention provides both for diffraction control, and for frequency compensation, and can provide the foregoing advantages.